1. Field of the Invention
The present invention relates to control systems for copying machines, and particularly to control systems for copying machines in which data for controlling copying machines are transmitted to a centralized control unit on a center side.
2. Description of the Related Art
A system for controlling a plurality of copying machines is disclosed in U.S. Pat. No. 4,583,834. In this disclosed system, various information of copying machines such as the total number of copies, troubles, remaining quantities of copy sheets and toner are transmitted to a computer. The computer processes the transmitted information and feeds back instructions to copying machines.
According to such a system, a plurality of copying machines supplied to users are connected to a centralized control unit through a communication network such as telephone liens for remote control of the copying machines. The centralized control unit is provided at a control base, and the controlling party receives with the centralized control unit the information transmitted from respective copying machines. Then, controlling works such as the issue of bills corresponding to the number of copies and dispatch of servicemen corresponding to the troubles are made.
Since general copying machines do not have functions of communicating with a centralized control unit through a communication network, a data terminal is attached to a copying machine for communication when configuring said system. This data terminal collects various information from the copying machine and communicates with the centralized control unit on the basis of the collected information.
The communication between each data terminal and the centralized control unit is made when predetermined conditions are satisfied. For example, when the current time comes to a predetermined time which is assigned to each data terminal, and also when a trouble of a copying machine occurs, each data terminal calls the centralized control unit. In this case, calls from a plurality of data terminals may overlap. Specifically, when a certain data terminal calls the centralized control unit in response to a trouble of the copying machine during the centralized control unit is in communication with another data terminal, the communication can not be established because the communication line is already occupied. Accordingly, the trouble of the copying machine can not be immediately informed to the centralized control unit, resulting in delay in taking care of the trouble by the management party.